PROJECT SUMMARY Global climate change and sea-level rise will influence the abundances and distributions of marine pathogens in coastal waters and seafood. This will result in a significant public health risk, which may lead to enhanced illness in exposed populations. Increasing incidences of human infections due to species of Vibrio, a marine Gram-negative opportunistic pathogen, have occurred from 1996-2010. The annual incidence rate of Vibrio illnesses in 2010 increased by 43% from those found during 2006-2008 and by 115% when compared to rates during 1996-1998. Exposures to Vibrio vulnificus causes more than 22 deaths annually and is the leading cause of death from seafood consumption accounting for approximately 95% of all deaths each year in the US alone. V. parahaemolyticus infections, while rarely fatal, exceed 8,000 cases annually. Despite the growing risk of these infections, little is known about how environmental parameters affect the complex virulence mechanisms involved in pathogenicity. With increasing rates of Vibrio infection expected to continue, there is an urgent need to fill this gap in knowledge related to how climate change may affect Vibrio virulence through adaptive evolution and altered gene expression. A long-term goal of this study is to understand how climate change influences Vibrio virulence. To accomplish this, experiments will determine how genetic mechanisms of V. vulnificus and V. parahaemolyticus virulence and antibiotic resistance are affected by changing environmental parameters. The central hypothesis (H1) is that Vibrio virulence and antibiotic resistance will increase under conditions simulating climate change. Through the coupling of mechanistic data to Vibrio abundance and distribution, forecast models may be enhanced and more accurately predict public health risk. Three specific aims will be addressed: (Aim 1) Determine how different combinations of environmental parameters (temperature, salinity, metals, nutrients) affect V. vulnificus and V. parahaemolyticus growth and viability. (Aim 2) Assess how altered growth conditions affect V. vulnificus and V. parahaemolyticus virulence using a Caenorhabditis elegans model of pathogenicity. (Aim 3) Determine the effect of altered growth conditions on V. vulnificus and V. parahaemolyticus gene expression. Our working hypothesis is that altered growth conditions will lead to upregulation of Vibrio stress response genes causing downstream changes in virulence gene expression. The results of this study can be incorporated into Vibrio forecast models to better predict spatial and temporal patterns of pathogenic Vibrio distribution. The enhanced model can then be used to guide better public health exposure controls and regulations.